Photodynamic therapy (PDT) of neoplastic disease is a new modality currently undergoing intense study. This project is designed to synthesize new photosensitizing dyes having absorbance at wavelengths greater than 650 nm for enhanced light penetration. A number of new sensitizers (called porphycene) have been made; they contain a tetrapyrrole macrocycle structure isomeric to porphyrin. Both monomeric and dimeric porphycenes are good photosensitizers, and their in vitro as well as in vivo PDT efficacy is being evaluated. The dimeric porphycenes havemw greater than 1000 Dalton; FAB-MS provided the necessary means for characterization of these compounds.